This invention relates to machine tools in general and, in particular, to lathes or like machines having a chuck with adjustable gripping jaws for holding work to be operated upon. The invention is directed more specifically to a chuck jaw changer for use on such a machine tool for automatically changing the gripping jaws of the chuck as required by the sizes of the work to be held thereby.
With the advent and dissemination of the numerical control (N/C or NC) technique, the metalworking industry has concentrated research and development efforts on the automation of all phases of machine tooling. The change of chuck jaws is no exception. A variety of devices have been suggested, some of which have been commercially accepted, for automatically changing the gripping jaws of chucks on lathes and other classes of machine tools.
A scheme common to such chuck jaw changers is the use of a jaw magazine of one type or another for holding sets of gripping jaws interchangeable with the jaw set on the chuck body. Typical conventional means for the transfer of the jaws between jaw magazine and chuck body is an arm pivoted medially similar to that of the familiar tool changer. The jaw transfer arm has a pair of gripping devices on its opposite ends for gripping the jaws on the jaw magazine and the chuck body and for changing them by the pivotal motion of the arm.
This and other comparable prior art chuck jaw changers have several drawbacks, however. One is that the jaw magazine and other associated parts must be machined to very stringent dimensional tolerances, and the magazine must be capable of indexing the jaws to the highest possible degree of accuracy for the proper transfer and positioning of the jaws on the jaw magazine and the chuck body. This of course adds considerably to the manufacturing costs of the jaw changers. The use of an additional actuator might be contemplated for exactly positioning the jaw magazine with respect to the chuck body. This alternative is also objectionable as the actuator would make the jaw changer too bulky.
The transfer of the gripping jaws between chuck body and jaw magazine by the pivotal arm is subject to the additional objection that the arm requires a large working space therebetween.
A further drawback concerns the jaw magazine itself, or its means for releasably holding the gripping jaws thereon. A typical conventional jaw magazine has any required number of undercut grooves formed at constant circumferential spacings therein for slidably receiving the T-shaped shoe portions of the gripping jaws. For preventing the gripping jaws from falling down, each undercut groove has a pair of spring energized retainer pins slidably engaged in bores in its wall so as to partly project therefrom into positive engagement with a series of teeth cut in the shoe portion of each jaw. The gripping jaws can be slid into and out of the undercut grooves by forcing the retainer pins into the walls against the effect of the springs. The retainer pins are prevented from falling out of the bores by keys embedded in the jaw magazine into sliding engagement with the retainer pins.
The above method of releasably holding gripping jaws on the jaw magazine is just about the simplest of the methods heretofore adopted to that end. The simplest known method, however, nevertheless requires the fabrication of the retainer pins and keys, the creation of the bores in the jaw magazine, and the insertion of the pins, keys and springs in the bores. Thus the manufacturing cost of the chuck jaw changer inevitably increases through an increase in the number of its component parts and in the time required for its assemblage. Further the mounting of many retainer pins, keys and springs on limited parts of the jaw magazine makes it difficult to create the undercut grooves therein at minimal angular spacings, resulting in an increase in the size of the jaw changer.
Any chuck jaw changer for installation on a machine tool should be as compact as possible to avoid interference with the operation of the machine tool itself. As machine tools have gained versatility in recent years, however, chuck jaw changers have become greater in size; indeed, some devices mounted on the headstocks of lathes occupy spaces close to the chuck or even to the tool post. Such bulky devices not only offer inconveniences to the machining operation but also are susceptible to the accumulation of chips or cuttings and to smearing with cutting oil, possibly resulting in malfunctioning or the marring of the gripping jaws or other parts.
Reduction in the size of the chuck jaw changer, however, presents no solution to the problem of chip or dust accumulation on the chuck body or on the gripping jaws thereon or on the jaw magazine. Such dirt can seriously impede the mounting of the gripping jaws on the chuck body, or may increase the resistance offered by the chuck body against the sliding motion of the jaws thereby making it impossible for the jaws to firmly grip and hold the work. This problem becomes all the more serious particularly if the chuck has toothed detents in its radial guideways for positive engagement with the toothed shoe portions of the gripping jaws. Chips caught in the teeth of the detents or in those of the jaw shoes can prevent their proper interengagement.